Drip Irrigation

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Drip irrigation can be the most efficient type of irrigation, but it is not suitable for all types of landscaping, and must be designed and installed carefully. In order to allow periodic flushing of debris, the layout of a drip irrigation system must be linear like a snake, not branching like a tree. The supply should provide for pressure control (if incoming pressure is significantly higher than 30 psi), flow control, pressure measurement, a filter and a flush bypass. If the supply pressure is high, the pressure control should be installed just before the flow control to avoid excessive pressure drop across the flow control.

As the drip hoses become fouled with deposits or debris, the pressure downstream of the flow control will rise. Since the flow control provides a reasonably constant flow despite variation in pressure, the pressure gauge will show increasing pressure as the drip hose becomes plugged. This indicates the need for flushing by opening a valve at the far end of the drip hose, and opening the flush bypass valve. In normal operation both of these valves will remain closed.

This setup is more complex than the arrangement recommended by most consumer irrigation outlets, but this is required to have a reliable, maintainable system which can be checked periodically for proper operation.

A porous hose provides one of the most reliable methods of dispensing water with a drip system since there are thousands of holes in the hose, making it less susceptible to plugging. Individual emitters are often used for drip systems and may be required in some places such as hanging pots, but they are prone to plugging even with filters installed. Laser drilled tubing is just as bad about plugging. The pressure control should be set to about 15 psi and the flow control should be sized to match the expected watering rate of the circuit. Be sure to buy porous hose with a known flow rate (gallons per hour per foot) or you will have no idea how much water you are applying!

If a continuous watering pattern is not needed, sections of porous hose can be replaced with PVC pipe as in the drawing below. Each drip station should be fed with one hose and should have a valve installed at the end that is used for periodic flushing.

Lay out the drip hoses like this.

DO NOT lay out the hose like this!!!

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